Kraus NEJM 2002 (1)

A link between physical activity and a reduced risk of cardiovascular disease exists. Whether the improvement is due to positive changes in lipoprotein profiles is undetermined. Using a prospective, randomized study design, researchers investigated the effects of the intensity and amount of exercise on lipoprotein profiles. The researchers gathered that the amount of exercise was the critical factor associated with improved lipoprotein profiles.

Researchers performed a prospective, randomized, controlled study comparing the effects of two different amounts and intensities of exercise training on lipoproteins. The ‘Studies of Targeted Risk Reduction Interventions through Defined Exercise’ investigated the effects of the amount and intensity of exercise on risk factors for cardiovascular disease in overweight and obese men and women with mild-to-moderate dyslipidemia. Subjects were gathered after giving written, informed consent. A total of 159 subjects who were sedentary, were overweight or mildly obese, and had dyslipidemia or an HDL cholesterol concentration below 40 mg per deciliter for men or below 45 mg per deciliter for women were recruited. Of the 159 randomized subjects, 48 dropped out of the study, 15 had an excessively low rate of adherence to exercise, 10 had incomplete lipid data, and 2 had excessive weight loss. In total, 84 subjects were left in the main analysis. Remaining subjects were randomly assigned to one of three exercise groups or a non-exercising control group. The three exercise groups were as follows: high-amount – high-intensity exercise, low-amount – high-intensity exercise, and low-amount – moderate-intensity exercise. These exercise prescriptions aimed to expend targeted amounts of kilocalories per kilogram of body weight. Goal expenditure for the high-amount – high-intensity prescription was 23 kcal per kilogram of body weight per week, and 14 kcal per kilogram per week for both low-amount groups. Exercise sessions were monitored by heart-rate monitors that provided recorded data or were directly observed. Nutrient intakes were determined at base line and at the end of the study. In order to minimize the confounding effects of weight loss, subjects were counseled to maintain body weight.

The findings suggest that regular exercise, even with minimal weight change, has broad beneficial effects on the lipoprotein profile. The greater amount of exercise and the degree of improvement in the lipoprotein profile showed a clear and consistent association. The higher amount of exercise had a greater beneficial effect on lipids and lipoproteins than the lower amount of exercise. Although the higher-intensity exercise showed improvements in the oxygen consumption levels, this proved less important when considering the lipoprotein profile responses. This means that the extensive improvements in the high-amount – high-intensity group were related to the amount, not the intensity, of physical activity. High-intensity exercise was related to greater oxygen consumption, but the high-amount – high-intensity exercise showed greater benefits in lipid-profiles than the low-amount – high-intensity exercise. Clearly, the duration of exercise was the important variable associated with an improved lipoprotein profile.

Detailed information was given regarding the characteristics of the subjects, exercise program, changes in body weight, fitness, and nutrient intake. Testing and reproducing the findings suggests that the conclusions made about duration of exercise being linked to improvements in lipoprotein profiles is reliable. However, researchers didn’t provide limitations to their findings. Further details regarding the types of proteins, fats, and carbohydrates consumed may have proven important. There have been links drawn between the protein source and improved lipoprotein profiles. Studies have also found links between low fat diets and worsening lipoprotein profiles. More details about the design of the study in regards to why they set up the nutrition and exercise program the way they did would be advantageous to understand this work. It’s understandable that the goal of the nutrition program was to maintain body weight. However, carbohydrates are the main source of fuel for the body during anaerobic activity, and fat is the main source of fuel for the body during aerobic activity. This includes sedentary behavior. There were high carbohydrate servings for both the experimental and control group. It’s natural to point to the need for consistency amongst experimental and control groups but low-carbohydrate diets negatively alter lipoprotein metabolism. The chances that researchers created a diet program that avoided the pitfalls associated with low-fat, low-carbohydrate diets seem unlikely. Credit to nutritional approaches to managing lipoprotein levels weren’t found in the references section. Other limitations were that benefits were associated with increased duration of exercise, rather than intensity. However, the fitness level of subjects increased proportionally to the duration of the exercise a long with the intensity. Since the high-intensity – high-amount exercise program improved fitness the most, and also required the largest amount of volume, there should be more comparison between the low-amount – high-intensity, and low-amount – moderate-intensity lipoprotein profiles. This would help rule out that increased duration a long with increased fitness level didn’t improve the lipoprotein profile. Another method could have been including a moderate-intensity – high-amount group to compare with the high-intensity – high-amount group. This would have better supported the increased duration link to improve lipoprotein profiles theory since there would be more comparisons available.

This article was particularly impressive. The amount of coherence between the information and results which tied everything nicely together was refreshing. Although a limitations section was void, the limitations of the study do not shine brightly. The research conducted a long with the information presented was clear, concise, and useful. From target heart rate, to the percentage of nutrients for each group, the information was included. I respect the amount of work put into this research. Lipoprotein profiles improved with increased physical activity. Is this the true cause of reduced cardiovascular disease? Further research will have to be conducted to know.

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